The microstructural stability of high temperature alloys is important in that precipitation of extraneous phases such as the topologically close packed phases sigma, mu, etc. or laves phase from an unstable alloy matrix is undesirable inasmuch as the extraneous precipitated phase can decrease strength, ductibility, fatigue resistance and impact resistance. Microstructural stability is usually measured by exposing an alloy to an elevated temperature for an extended period of time such as 1,000 hours, and metallographically examining the exposed sample for the presence of any extraneous phases. Alloy stability is usually correlated with electron vacancy number N.sub.v, and it is usually considered by those skilled in the art that the alloy is unstable when the electron vacancy number exceeds a critical value.
Accordingly, it is desirable to reduce the precipitation of extraneous phases, and in particular, the sigma phase for enhancement of microstructural stability of high temperature nickel-base alloys.